As prior-art examples of structures related to lubrication in a scroll compressor of the type in which the pressure on the discharge side acts on the electric motor, the lubricating oil sump, etc., reference will be made to Japanese Patent Publication No. 61-19803 (Lubricating Device in a Scroll Fluid Machine) and the specification of U.S. Pat. No. 4,552,518 (Scroll Machine). FIG. 1 shows the structure of the scroll compressor disclosed in Japanese Patent Publication No. 61-19803 mentioned above, which includes a closed container 101, which contains a compression mechanism 102, an electric-motor stator 103 fixed in position therebelow, and further below the same, a lubricating oil sump 104 for gathering lubricating oil. The compression mechanism 102 comprises: a stationary scroll wrap member 107 having a stationary scroll wrap 106 which is integrally formed on a stationary end plate 105; an orbiting scroll wrap member 110 having an orbiting scroll wrap 108 which is formed on an orbiting end plate 109 and which is engaged with the stationary scroll wrap 106 so as to define a plurality of compression chambers 111; a rotation restraining member 112 which prevents the orbiting scroll wrap member 110 from rotating so as to allow it to make an orbiting movement only; a crankshaft 115 having an eccentric drive shaft 114 which is adapted to cause an orbiting drive shaft 113 provided on the orbiting end plate 109 to make an eccentric orbiting movement; a bearing member 119 having a first and second main shaft bearing 117 and 118 which support a main shaft 116 of the crankshaft 115; etc. Further, a frame body plane 120 on the orbiting-end-plate side of the stationary end plate 105 and an orbiting-end-plate surface 121 on the stationary-end-plate side of the orbiting end plate 109 are so arranged as to slidably abut against each other, and, at the same time, an intermediate pressure hole 122 communicating with the compression chambers 111 is provided in the orbiting end plate 109 so as to keep the pressure in a back-pressure chamber 123 on that side of the orbiting end plate 109 which is opposite to the orbiting scroll wrap 108 at a pressure level which is intermediate between the discharge pressure and the intake pressure. Refrigerant gas, sucked into the compression mechanism 102 through an intake pipe 124 of the compressor, is compressed in the compression chambers 111, and then discharged through a discharge outlet 125. It then passes through a peripheral passage 126 around the compression chambers 111 and is discharged to the exterior of the compressor through a discharge pipe 127. The lubricating oil in the lubricating oil sump 104 is supplied by way of an eccentric oil feeding path 129 extending through the main shaft 116 of the crankshaft 105 and a first branch oil feeding path to the second main shaft bearing 118. That portion of the lubricating oil which flows through the oil feeding path 129 and a second branch oil feeding path 131 passes through an oil groove on the outside of the main shaft 116 and lubricates the first main shaft bearing 117 before it reaches the back-pressure chamber 123. The lubricating oil supplied to the bottom portion 133 of the orbiting drive bearing 113 after passing through the eccentric oil feeding path 129 undergoes pressure reduction in the gap between the eccentric drive shaft 114 and the orbiting drive bearing 113 and is discharged into the back-pressure chamber 123. The lubricating oil which is in the back-pressure chamber 123 passes through the intermediate pressure hole 122, etc. and flows through the compression chambers 111, where it is compressed and discharged out of the compression mechanism along with the refrigerant. That is, all of the lubricating oil which has lubricated the first main shaft bearing 117 and the orbiting drive bearing 113 ultimately enters the compression chambers 111. FIG. 2 is a sectional view showing the structure of the scroll compressor which is disclosed in the specification of U.S. Pat. No. 4,552,518, and FIG. 3 is an enlarged view showing a part of the same. A closed container 201 contains a compression mechanism 202, below which the stator of an electric motor 203 is fixed in position, and, provided further below the same is a lubricating oil sump 204 for gathering lubricating oil. The compression mechanism 202 comprises: a stationary scroll wrap member 207 having a stationary scroll wrap 206 which is integrally formed on a stationary end plate 205; an orbiting scroll wrap member 210 having an orbiting scroll wrap 208 which is formed on an orbiting end plate 209 and which is engaged with the stationary scroll wrap 206 so as to define a plurality of compression chambers 211; a rotation restraining member 212 which prevents the orbiting scroll wrap member 210 from rotating so as to allow it to make an orbiting movement only; a first and a second bearing member 219 and 219a which respectively support a first and a second main shaft 216 and 216a of a crankshaft 215, which has an eccentric drive bearing 214 that is adapted to cause an orbiting drive shaft 213 provided on the orbiting end plate 209 to make an eccentric orbiting movement; etc. The closed container 201 is divided by a supporting frame body 220 provided in the compression mechanism 202 into an upper section which constitutes an intake chamber 221 where intake pressure is predominant and a lower section which constitutes a discharge space 222 where discharge pressure is predominant. Further, there is provided an annular sealing band 224 which slidably abuts against an orbiting-end-plate back surface 223 on that side of the orbiting end plate 209 which opposite to the orbiting scroll wrap 208 and which divides this orbiting-end-plate back surface 223 into a surface in the central portion upon which the pressure of the discharge gas acts and a surface upon which a pressure lower than the discharge pressure acts. Further, the lubricating oil in the lubricating oil sump 204 is led through an oil feeding capillary tube 225 to an inlet 226 of the compression mechanism 202, and is compressed in the compression chambers 211 together with the refrigerant gas sucked into the compression mechanism 202 through an inlet pipe 211 of the compressor. Afterwards, it is discharged through a discharge hole 228 which is provided in the orbiting drive shaft 213, and is centrifugally separated from the discharged refrigerant gas in an oil separation chamber 229 provided in the crankshaft 215. Then, it passes from the eccentric bearing 214 and by the the vicinity of the orbiting-end-plate back surface 223 and is supplied to the first main shaft bearing 217. Meanwhile, the discharge refrigerant gas having left the oil separation chamber 229 cools the electric motor 203 as indicated by the arrows, and is then discharged out of the compressor through a discharge pipe 230.
In both of the above-described scroll compressors, a high bearing load is applied to the orbiting drive bearing, the eccentric bearing, the first main shaft bearing, etc., so that a high lubricating-oil flow rate is needed. However, the flow rate at which lubricating oil is supplied to these bearings can only be equal to or lower than the flow rate at which it is supplied to the compression chambers, with the result that lubricating oil is supplied to the compression chambers at an excessive flow rate. However, the lubricating oil sump is situated in the discharge space, so that it is at a high temperature and contains a considerable amount of refrigerant. Accordingly, if lubricating oil enters the compression chambers at an excessive flow rate, the efficiency of the compressor is materially deteriorated by the quantity of heat this lubricating oil possesses and this refrigerant. Suppose, for example, the flow rate at which lubricating oil enters the compression chambers is set at a large value in order to prevent these bearings from being damaged or a large bearing loss from being generated during high speed operation. Then, the flow rate of lubricating oil remains high even when the compressor is being operated at low speed because the flow rate of lubricating oil depends upon the difference between the pressure in the back-pressure chamber and the discharge pressure, with the result that the flow rate of lubricating oil with respect to the discharge amount becomes excessively high, thus materially deteriorating the compressor efficiency. Apart from this, compressors for room air conditioners nowadays are in many cases made in a minimum closed-container body diameter with a view to meeting the demand for a reduction in size and weight, with the stator of the electric motor being directly fixed to the inner wall. In a compressor having such a reduced body diameter, on the other hand, the diameter of the lubricating oil sump is also naturally small, with the result that the height of the lubricating oil level greatly varies depending on the operating condition. In such a case, it is necessary to arrange the discharge pipe at a position spaced away from the lubricating oil sump in order to prevent a large amount of lubricating oil from being taken out from this discharge pipe. Accordingly, in a compressor of the type in which the electric motor is arranged below the compression mechanism and the closed container of which has a relatively small outer diameter, the discharge pipe must be arranged above the electric motor, as in Japanese Patent Publication No. 61-19803 mentioned above. In such a compressor, however, arranging the discharge pipe above the electric motor entails the following the problem: Since the discharge outlet of the compression mechanism is above the electric motor, it takes a very complicated structure to form a discharge-refrigerant-gas passage which will bring the discharged refrigerant upwards again by way of the portion below the electric motor to discharge it out of the compressor through the discharge pipe. In the lubrication system according to Japanese Patent Publication No. 61-19803 mentioned above, the centrifugal force generated by the rotation of the eccentric oil feeding path is rather weak when the rotating speed of the electric motor is low, so that, in some cases, an oil pressure which is high enough to allow the oil to reach the first branch oil feeding path cannot be obtained. In such a case, there is the danger of the refrigerant gas in the discharge space flowing backwards through the bearing gap in the second main shaft bearing or the oil feeding passage into the first-branch oil feeding path, thereby hindering the lubrication. In the case of the example shown in the specification of U.S. Pat. No. 4,552,518 mentioned above, the oil feeding passage leading to the eccentric bearing 214, the end-plate back surface 223, and the first main shaft bearing 217, is filled with a small amount of lubricating oil and a large amount of discharged refrigerant air, which have been separated from each other in the oil separation chamber 229, so that a large amount of gas exist on the high pressure side which is inside the annular sealing band 224. As a result, the sealing effect of the annular sealing band degenerates to allow a large amount of discharged refrigerant gas to leak towards the compression chambers, thereby hindering the normal operation of the compressor, deteriorating the compressor efficiency, etc. Further, even if a large amount of lubricating oil can be supplied to the end surface of the main shaft of the crankshaft in a structure in which an eccentric bearing is arranged inside the main shaft of the crankshaft, as in the specification of U.S. Pat. No. 4,552,518 mentioned above, by an appropriate means different from that of this patent, a high pressure will be generated in that portion of the lubricating oil which is around the outer periphery of the main shaft by the rotation of the end surface of the main shaft when the operating speed of the compressor is high, so that if the oil feeding passage of the main shaft opens there, a large amount of lubricating oil may flow disproportionately through that oil feeding passage, resulting in a shortage in the amount of oil that is fed to the eccentric bearing on the inside.